The invention relates to a method and apparatus for detecting defects which is adapted to detect a condition of occurrence of defects, such as foreign matter, in a manufacturing process of, for example, a semiconductor device, a liquid crystal display element, a printed board, or the like. The manufacturing process involves detecting a defect, e.g., foreign matter, caused in a step of forming a pattern on a substrate so as to manufacture an object of interest, and analyzing and remedying the defect.
In the conventional semiconductor manufacturing process, the presence of foreign matter on a semiconductor substrate (a substrate of interest to be inspected) may cause failures, including an electrical insulation failure, and short-circuit of wiring. Furthermore, when a semiconductor element is miniaturized to cause fine foreign matter in the semiconductor substrate, this foreign matter may cause the electrical insulation of a capacitor, or a breakage of a gate oxide film or the like. Such foreign matter may occur due to various causes, for example, from a movable part of a conveying device, from a human body, from a reaction with a process gas within a processing chamber, or from contaminant into a chemical agent or a material, and may be trapped into the semiconductor substrate in various forms.
Also, in the similar manufacturing process of the liquid crystal display element, the presence of any defects, such as contamination by foreign matter onto the pattern, may render the display element useless. The same holds true for the manufacturing process of the printed board, that is, the contamination by foreign matter may cause the short-circuit of the pattern, and the defective connection.
One of these kinds of conventional techniques for detecting foreign matter on a semiconductor substrate involves detecting scattered light generated from foreign matter by irradiating the semiconductor substrate with a laser beam when the foreign matter is attached thereto, and comparing a result of this detection with a result, of previous detection of the same kind of semiconductor substrate, as disclosed in, for example, JP-A No. 89336/1987. This technique can eliminate misinformation due to the pattern, and detect the foreign matter and defects with high sensitivity and high reliability. As disclosed in, for example, JP-A No. 135848/1988, another technique is known which involves detecting  scattered light generated from foreign matter by irradiating a semiconductor substrate with a laser beam when the matter is attached thereto, and analyzing the detected foreign matter using an analysis technique, such as a laser photo luminescence, or a two-dimensional X-ray analysis (XMR).
As another technique for detecting foreign matter, JP-A No. 218163/1993, and JP-A No. 258239/1994 disclose a method for detecting foreign matter and defects which involves irradiating a substrate of interest to be inspected, with coherent light linearly formed, removing the reflected and scattered light from a repetitive pattern on the substrate with a spatial filter, and emphasizing and detecting the nonrepetitive foreign matter and defects.
Furthermore, a foreign matter detector is known in JP-A No. 117024/1989 which is adapted to irradiate a circuit pattern formed on the substrate of interest to be inspected, from the direction of an inclined angle of 45 degrees with respect to a main group of lines of the pattern such that the 0-order diffracted light from the main group of lines does not enter an aperture of an objective lens. The '163 patent discloses that diffracted light from a group of lines other than the main group of lines is also blocked by a spatial filter.
Other conventional techniques relating to a method and apparatus for detecting defects including foreign matter or the like are known in, for example, JP-A 324003/1994, JP-A 271437/1996, and U.S. Pat. No. 6,608,676.
In all the disclosures of the above-mentioned documents, however, a signal indicative of defects is missed due to scattered light from an irregular circuit pattern part, resulting in low sensitivity. On a transparent film, such as an oxide film, through which illuminating light passes, the brightness of the scattered light from the pattern is varied by a change in film thickness, which may further result in the lower sensitivity.